Enhanced anti-parallel-pinned sensor using thin ruthenium spacer and high magnetic field annealing

ABSTRACT

An anti-parallel pinned sensor is provided with a spacer that increases the anti-parallel coupling strength of the sensor. The anti-parallel pinned sensor is a GMR or TMR sensor having a pure ruthenium or ruthenium alloy spacer. The thickness of the spacer is less than 0.8 nm, preferably between 0.1 and 0.6 nm. The spacer is also annealed in a magnetic field that is 1.5 Tesla or higher, and preferably greater than 5 Tesla. This design yields unexpected results by more than tripling the pinning field over that of typical AP-pinned GMR and TMR sensors that utilize ruthenium spacers which are 0.8 nm thick and annealed in a relatively low magnetic field of approximately 1.3 Tesla.

RELATED APPLICATIONS

This application is a Continuation of co-pending U.S. patent applicationSer. No. 11/048,406 entitled ENHANCED ANTI-PARALLEL-PINNED SENSOR USINGTHIN RUTHENIUM SPACER AND HIGH MAGNETIC FIELD ANNEALING, filed on Feb.1, 2005, which is incorporated herein by reference as if fully set forthherein.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates in general to and, in particular, to animproved system, method, and apparatus for improving the pinningstrength of anti-parallel (AP) pinned giant magnetoresistive (GMR) andtunneling magnetoresistive (TMR) sensors using extra thin, ruthenium(Ru) alloy spacers that are annealed in a high magnetic field.

2. Description of the Related Art

A spin valve type giant magnetoresistive thin film used for a magneticrecording head of a hard disk drive has a multilayer film structurecomprised of a plurality of layers or thin films. These layers includean antiferromagnetic layer, a fixed magnetization layer, a nonmagneticconductive layer, and a free magnetization layer. In the multilayer filmstructure of the spin valve type giant magnetoresistive thin film, thenonmagnetic conductive layer is formed between the fixed magnetizationlayer and the free magnetization layer so that the two are isolated bythe nonmagnetic conductive layer. Further, since the antiferromagneticlayer is made to adjoin the fixed magnetization layer, the magneticmoment of the fixed magnetization layer is fixed in one direction by theexchange coupling with the antiferromagnetic layer. On the other hand,the magnetic moment of the free magnetization layer is freely rotated inaccordance with the external magnetic field.

The spin valve type giant magnetoresistive thin film generates theso-called “giant magnetoresistive effect,” or the change of theelectrical resistance due to the relative angle formed by the magneticmoment of the fixed magnetization layer and the magnetic moment of thefree magnetization layer. The rate of change of the electricalresistance due to the giant magnetoresistive effect is called the“magnetoresistive ratio” (MR ratio). The MR ratio of a spin valve typegiant magnetoresistive thin film is far higher than that of aconventional anisotropic magnetoresistive thin film.

There are three types of spin valve type giant magnetoresistive thinfilms. The first type is known as a “bottom type” and comprises, from asubstrate side, a buffer layer, an antiferromagnetic layer, a fixedmagnetization layer, a nonmagnetic conductive layer, a freemagnetization layer, and a protective layer that are stacked in thatorder. The second type is known as a “top type” and comprises asubstrate, a buffer layer, a free magnetization layer, a nonmagneticconductive layer, a fixed magnetization layer, an antiferromagneticlayer, and a protective layer in that order. The third type is called a“dual type” and comprises a substrate, a buffer layer, a firstantiferromagnetic layer, a first fixed magnetization layer, a firstnonmagnetic conductive layer, a free magnetization layer, a secondnonmagnetic conductive layer, a second fixed magnetization layer, asecond antiferromagnetic layer, and a protective layer in that order.

There have been proposed thin films for replacing the single layers ofthe fixed magnetization layers with synthetic ferromagnetic structureshaving fixed magnetization layer elements, nonmagnetic layers, and fixedmagnetization layer elements. Furthermore, the free magnetization layeralso comes in single layer structures and multilayer structures. In freemagnetization layers and fixed magnetization layers of multilayerstructures, all the layers are magnetic films, but sometimes differentmagnetic films are stacked or a sandwich stricture interposing anonmagnetic film therebetween is used.

The giant magnetoresistive effect of spin valve type giantmagnetoresistive thin film is due to spin-dependent scattering ofconductive electrons at the stacked interfaces of multilayer films.Therefore, to obtain a high MR ratio, cleanliness or flatness of theinterfaces becomes important in the process of production of the spinvalve film. Therefore, in the spin valve type giant magnetoresistivethin film, to achieve the cleanliness or flatness of the interfaces, thefilms are often formed continuously in the same vacuum chamber so thatthe intervals between formations of one layer and another become asshort as possible.

Techniques for forming a film in vacuum include magnetron sputtering,ion beam sputtering, electron cyclotron resonance (ECR) sputtering,facing target sputtering, high frequency sputtering, electron beamevaporation, resistance heating evaporation, molecular beam epitaxy(MBE), etc.

To obtain a high MR ratio, the thickness of the nonmagnetic conductivelayer should be small so as to suppress the flow of conductive electronsnot contributing to the giant magnetoresistive effect (shunt effect). Ifthe thickness of the nonmagnetic conductive layer is made small,however, the fixed magnetization layer and the free magnetization layerwill end up coupling ferromagnetically through the nonmagneticconductive layer. The interlayer coupling magnetic field between thefixed magnetization layer and the free magnetization layer should besmall for practical use of the magnetic recording head of a hard diskdrive. In the past, to reduce the interlayer coupling magnetic field,the thickness of the nonmagnetic conductive layer was set to 2.5 to 3.5nm.

The technique of reducing the ferromagnetic coupling occurring betweenthe fixed magnetization layer and the free magnetization layer byinserting a nano oxide layer of a size of not more than 1 nm into thefixed magnetization layer in the bottom type of spin valve film has beenproposed. As a result, a relatively small interlayer coupling magneticfield is obtained and a high MR ratio is obtained even with a thin (2.0to 2.5 nm) nonmagnetic conductive layer. That is, in the conventionalspin valve type giant magnetoresistive thin film, the thickness of thenonmagnetic conductive layer was set thick (2.5 to 3.5 nm) to reduce theinterlayer coupling magnetic field, but the problem arose of a flow ofconductive electrons not contributing to the giant magnetoresistiveeffect (shunt effect) and the MR ratio ending up being reduced. Further,in the process of production of the above nano oxide layer, an oxidationstep becomes necessary in the middle of formation of the fixedmagnetization layer. An oxidation step is complicated and is poor inreproducibility. Thus, an improved solution would be desirable.

SUMMARY OF THE INVENTION

One embodiment of a system, method, and apparatus for increasing theanti-parallel coupling strength of an anti-parallel pinned sensor isdisclosed. The present invention includes an anti-parallel pinnedsensor, such as a GMR or TMR sensor, having a pure ruthenium orruthenium alloy spacer. The thickness of the spacer is less than 0.8 nm,preferably between 0.1 and 0.6 nm. The spacer is also annealed in amagnetic field that is 1.5 Tesla or higher. In one embodiment, themagnetic field is 5 Tesla or more. The present invention yieldsunexpected results by more than tripling the pinning field over that oftypical AP-pinned GMR and TMR sensors that utilize ruthenium spacerswhich are 0.8 nm thick and annealed in a relatively low magnetic fieldof approximately 1.3 Tesla.

The foregoing and other objects and advantages of the present inventionwill be apparent to those skilled in the art, in view of the followingdetailed description of the present invention, taken in conjunction withthe appended claims and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the features and advantages of theinvention, as well as others which will become apparent are attained andcan be understood in more detail, more particular description of theinvention briefly summarized above may be had by reference to theembodiment thereof which is illustrated in the appended drawings, whichdrawings form a part of this specification. It is to be noted, however,that the drawings illustrate only an embodiment of the invention andtherefore are not to be considered limiting of its scope as theinvention may admit to other equally effective embodiments.

FIG. 1 is a schematic sectional view of a multilayer structure of abottom type, spin valve type giant magnetoresistive thin film for amagnetic recording head in a disk drive;

FIG. 2 are plots of spacer layer thicknesses versus pinning fieldstrength for various embodiments of a sensor constructed in accordancewith the present invention;

FIG. 3 is a high level flow diagram of a method in accordance with thepresent invention; and

FIG. 4 is a schematic drawing of a hard disk drive constructed inaccordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, one embodiment of a multilayer structure of abottom type of a spin valve type giant magnetoresistive (GMR) thin filmof a multilayer film is shown. According to this embodiment of themultilayer structure, Ta (3 nm)/NiFe (2 nm)/PtMn (12 nm)/CoFe (1.8nm)/Ru/CoFe (2.8 μm)/Cu (2.2 nm)/CoFe (1.5 nm)/NiFe (2.5 nm)/Cu (1nm)/Ta (3 nm) are consecutively stacked in that order from the substrate25 side. The numerical values given in parentheses in the layers are thethicknesses of the layers in units of nanometers (nm). One skilled inthe art will recognize that these numerical values are given by way ofexample and for reference purposes for one embodiment of the presentinvention. The present invention is not limited to such values.

In one embodiment of the present invention, the Ru film or spacer isless than 0.8 nm thick, and preferably between the range of 0.1 and 0.6nm. The Ru spacer is also annealed in a high magnetic field that isgreater than 1.5 Tesla, and, in one embodiment, greater than 5 Tesla. Inyet another embodiment, the spacer is annealed in a magnetic field from5 to 10 Tesla.

In this multilayer structure, Ta (3 nm) and NiFe (2 nm) are the bufferlayers 41, PtMn (12 nm) is the antiferromagnetic layer 42, CoFe (1.8nm), Ru, and CoFe (2.8 nm) are the fixed magnetization layers (syntheticferromagnetic structure) 43, Cu (2.2 nm) is the nonmagnetic conductivelayer 44, CoFe (1.5 nm) and NiFe (2.5 nm) are the free magnetizationlayers 45, Cu (nm) is a spin filter 46, and Ta (3 nm) is the protectivelayer 47. These layers may be formed in one or more film formingchambers. Plasma treatment is suitably performed in the film formingsteps. When performing plasma treatment, the film formation istemporarily interrupted at the desired interface, the substrate 25 istransported to a plasma treatment chamber for plasma treatment.

Referring now to FIG. 2, plots of spacer layer thicknesses versuspinning field strength for four embodiments of a sensor (e.g., amagnetic sensor) constructed in accordance with the present inventionare shown. Plot 21 depicts performance for a pure ruthenium spacer, plot23 is that of a ruthenium alloy having 9.2% CoFe, plot 25 is that of aruthenium alloy having 27.9% CoFe, and plot 27 is that of a rutheniumalloy having 33.6% CoFe. The strength of the pinning field clearlyincreases for each of these embodiments at spacer thicknesses that areless than 0.8 nm, and dramatically increases at thicknesses of less than0.6 nm.

Referring now to FIG. 3, a simplified, high level flow chart depictingone embodiment of a method of the present invention is shown. Forexample, the method starts as illustrated at step 301, and increases theanti-parallel coupling strength of an anti-parallel pinned sensor. Themethod comprises providing a ruthenium spacer having a thickness of lessthan 0.8 nm, as depicted at step 303, forming an anti-parallel pinnedsensor with the ruthenium spacer (step 305), and annealing the rutheniumspacer in a magnetic field that is 1.5 Tesla or higher (step 307). Theanti-parallel pinned sensor may be selected from the group consisting ofGMR and TMR sensors. The ruthenium spacer may comprise pure ruthenium,or a ruthenium alloy formed with, for example, Co, Fe, CoFe, and/orother similar types of metals. In one embodiment, the thickness of theruthenium spacer is between 0.1 and 0.6 nm and die magnetic field isgreater than 5 Tesla.

Referring now to FIG. 4, one embodiment of the present invention isprovided in a magnetic hard disk file or drive 111 for a computersystem. Drive 111 has an outer housing or base 113 containing at leastone magnetic disk 115. Disk 115 is rotated by a spindle motor assemblyhaving a central drive hub 117. An actuator 121 comprises a plurality ofparallel actuator arms 125 (one shown) in the form of a comb that ispivotally mounted to base 113 about a pivot assembly 123. A controller119 is also mounted to base 113 for selectively moving the comb of arms125 relative to disk 115.

In the embodiment shown, each arm 125 has extending from it at least onecantilevered load beam and suspension 127. A magnetic read/writetransducer or head (equipped with the sensor described above) is mountedon a slider 129 and secured to a flexure that is flexibly mounted toeach suspension 127. The read/write heads magnetically read data fromand/or magnetically write data to disk 115. The level of integrationcalled the head gimbal assembly is head and the slider 129, which aremounted on suspension 127. The slider 129 is usually bonded to the endof suspension 127. The head is typically pico size (approximately1250×1000×300 microns) and formed from ceramic or intermetallicmaterials. The head also may be femto size (approximately 850×700×230microns) and is pre-loaded against the surface of disk 115 (in the rangetwo to ten grams) by suspension 127.

Suspensions 127 have a spring-like quality which biases or urges the airbearing surface of the slider 129 against the disk 115 to enable thecreation of the air bearing film between the slider 129 and disksurface. A voice coil 133 housed within a conventional voice coil motormagnet assembly 134 (top pole not shown) is also mounted to arms 125opposite the head gimbal assemblies. Movement of the actuator 121(indicated by arrow 135) by controller 119 moves the head gimbalassemblies radially across tracks on the disk 115 until the heads settleon their respective target tracks. The head gimbal assemblies operate ina conventional manner and always move in unison with one another, unlessdrive 111 uses multiple independent actuators (not shown) wherein thearms can move independently of one another.

While the invention has been shown or described in only some of itsforms, it should be apparent to those skilled in the art that it is notso limited, but is susceptible to various changes without departing fromthe scope of the invention.

1. A method of increasing the coupling strength of a sensor, the methodcomprising: (a) providing a ruthenium spacer having a thickness of lessthan 0.8 nm; (b) forming a sensor with the ruthenium spacer; and (c)annealing the ruthenium spacer in a magnetic field that is 1.5 Tesla orhigher.
 2. The method of claim 1, wherein the sensor is an anti-parallelpinned sensor.
 3. The method of claim 1, wherein the sensor is selectedfrom the group consisting of GMR and TMR sensors.
 4. The method of claim1, wherein the ruthenium spacer is a ruthenium alloy.
 5. The method ofclaim 1, wherein the ruthenium spacer is pure ruthenium.
 6. The methodof claim 1, wherein the thickness of the ruthenium spacer is between 0.1and 0.6 nm.
 7. The method of claim 1, wherein the magnetic field is from5 to 10 Tesla.
 8. A method of increasing the anti-parallel couplingstrength of an anti-parallel pinned sensor, the method comprising: (a)providing a ruthenium spacer having a thickness of less than 0.8 nm; (b)forming an anti-parallel pinned sensor with the ruthenium spacer; and(c) annealing the ruthenium spacer in a magnetic field that is 1.5 Teslaor higher.
 9. The method of claim 8, wherein the anti-parallel pinnedsensor is selected from the group consisting of GMR and TMR sensors. 10.The method of claim 8, wherein the ruthenium spacer is a rutheniumalloy.
 11. The method of claim 8, wherein the ruthenium spacer is pureruthenium.
 12. The method of claim 98 wherein the thickness of theruthenium spacer is between 0.1 and 0.6 nm.
 13. The method of claim 8,wherein the magnetic field is from 5 to 10 Tesla.
 14. A hard disk drive,comprising: a magnetic disk; an actuator having a head for reading datafrom and writing data to the disk, the head including an anti-parallelpinned sensor with a ruthenium spacer having a thickness of less than0.8 nm, and the ruthenium spacer having an annealed treatment from amagnetic field that is 1.5 Tesla or higher.
 15. The hard disk drive ofclaim 14, wherein the anti-parallel pinned sensor is selected from thegroup consisting of GMR and TMR sensors.
 16. The hard disk drive ofclaim 14, wherein the ruthenium spacer is a ruthenium alloy.
 17. Thehard disk drive of claim 14, wherein the ruthenium spacer is pureruthenium.
 18. The hard disk drive of claim 14, wherein the thickness ofthe ruthenium spacer is between 0.1 and 0.6 nm.
 19. The method of claim14, wherein the magnetic field is from 5 to 10 Tesla.